عَنِ ابْنِ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ ((مَنِ اسْتَعَاذَ بِاللَّهِ فَأَعِيذُوهُ وَمَنْ سَأَلَكُمْ بِاللَّهِ فَأَعْطُوهُ وَمَنْ دَعَاكُمْ فَأَجِيبُوهُ وَمَنْ أَتَى عَلَيْكُمْ مَعْرُوفًا فَكَافِئُوهُ فَإِنْ لَمْ تَجِدُوا مَا تُكَافِئُوهُ فَادْعُوا لَهُ حَتَّى تَعْلَمُوا أَنْ قَدْ كَافَأْتُمُوهُ))
It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: Whoever seeks refuge by invoking Allah, grant him refuge; whoever asks you in the name of Allah, give to him; whoever invites you, accept his invitation; and whoever does a good deed to you, repay him. If you do not have anything to repay him with, then pray for him so much that you feel you have repaid him.